Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
  • C03C14/002—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix the non-glass component being in the form of fibres, filaments, yarns, felts or woven material
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/14—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on silica
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/71—Ceramic products containing macroscopic reinforcing agents
  • C04B35/78—Ceramic products containing macroscopic reinforcing agents containing non-metallic materials
  • C04B35/80—Fibres, filaments, whiskers, platelets, or the like
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/02—Fibres; Filaments; Yarns; Felts; Woven material
  • C03C2214/03—Fibres; Filaments; Yarns; Felts; Woven material surface treated, e.g. coated
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/20—Glass-ceramics matrix
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249967—Inorganic matrix in void-containing component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249967—Inorganic matrix in void-containing component
  • Y10T428/249969—Of silicon-containing material [e.g., glass, etc.]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249967—Inorganic matrix in void-containing component
  • Y10T428/24997—Of metal-containing material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249986—Void-containing component contains also a solid fiber or solid particle
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249987—With nonvoid component of specified composition
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249987—With nonvoid component of specified composition
  • Y10T428/24999—Inorganic
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2916—Rod, strand, filament or fiber including boron or compound thereof [not as steel]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2918—Rod, strand, filament or fiber including free carbon or carbide or therewith [not as steel]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
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  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2918—Rod, strand, filament or fiber including free carbon or carbide or therewith [not as steel]
  • Y10T428/292—In coating or impregnation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/2938—Coating on discrete and individual rods, strands or filaments
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/294—Coated or with bond, impregnation or core including metal or compound thereof [excluding glass, ceramic and asbestos]

Definitions

• the present invention relates to novel ceramic matrix composites using modified hydrogen silsesquioxane resin as the matrix for refractory fibers. These composites can be formed into complex shapes which have good oxidation resistance at high temperatures, high strength and toughness.
• Ceramic matrix composites and methods for their production are well known in the art. For instance, several recent review articles such as Mah et al., Ceramic Bulletin, Vol. 66, No. 2 (1987), and Schioler et al., Ceramic Bulletin, Vol. 65, No. 2 (1986), describe various matrices and fibers used in ceramic matrix composites as well as a variety of processing techniques used for their production. The composite materials and methods described in these references, however, differ from those described herein.
• Hydrogen silsesquioxane resin is also known in the art. For instance, Collins et al. in U.S. Pat. No. 3,615,272 describe the production of soluble hydrogen silsesquioxane resin by the hydrolysis and condensation of a silane in a sulfuric acid medium. Similarly, Haluska et al. in U.S. Pat. No. 4,756,977 teach the use of hydrogen silsesquioxane resin to form protective ceramic coatings on electronic devices. These references, however, do not describe the modification of the resin nor the use of the resin as a matrix precursor in ceramic matrix composites.
• modified hydrogen silsesquioxane resin can be used to prepare ceramic matrix composites with excellent properties.
• the present invention relates to a method of making fiber reinforced ceramic matrix composites.
• the method comprises impregnating coated fibers with a matrix precursor mixture comprising modified hydrogen silsesquioxane resin and, optionally, ceramic fillers.
• the impregnated fibers are formed into the desired shape and cured to form a molded part.
• the molded part is then heated to a temperature of at least about 1000° C. in an inert atmosphere for a time effective to convert the matrix precursor mixture to a ceramic.
• composites derived in the above manner can be reimpregnated with the matrix precursor mixture to decrease the open porosity.
• the present invention is based on the discovery that novel ceramic matrix composites may be formed using modified hydrogen silsesquioxane resin as the matrix precursor. This was particularly unexpected since hydrogen silsesquioxane resin does not have carbon in its repeating units and high carbon levels were thought to be essential in the fabrication of desirable composites. The present inventor has now found that the present composites containing small amounts of carbon have excellent strength and toughness even at elevated temperatures in air.
• the refractory fibers which may be used in this invention comprise any high-modulus fibers which are compatible with the modified hydrogen silsesquioxane resin, matrices and any fiber coatings described herein and which can withstand the polymer infiltration processing. Many of these fibers are known in the art and many are commercially available. Examples of suitable fibers include those of silicon carbide, silicon nitride, silicon carbide deposited on a carbon core, aluminum borate, aluminum oxide, silicon oxide, silicon carbide containing titanium, silicon oxycarbides, silicon oxycarbonitrides, carbon and the like. Generally, such fibers should have a modulus greater than about 100 GPa, preferably greater than 150 GPa. These fibers may contain any desirable number of filaments per tow and have a size in the range of about 5 micrometers to about 500 micrometers.
• fibers examples include silicon carbide fibers with a diameter in the range of 10-20 micrometers manufactured by Nippon Carbon and sold under the trade name "Nicalon”; fibers comprising silicon carbide deposited on a carbon core with a diameter of about 143 micrometers manufactured by Avco and designated “SCS-6"; alumina-boria-silica fibers with a diameter of about 10-12 micrometers manufactured by 3M and sold under the tradenames "Nextel 312", “Nextel 440" and “Nextel 480”; Al203 fibers with a diameter of about 20 micrometers manufactured by Du Pont under the designation "FP”; SiO 2 fibers with a diameter of about 8-10 micrometers manufactured by J. P.
• any of the above fibers are functional, those preferred herein comprise ceramic fibers of silicon, carbon, nitrogen and/or oxygen. Especially preferred are "Nicalon" silicon oxycarbide fibers and crystalline silicon carbide fibers.
• fibers may be used in nearly any length and may be arranged in the matrix in nearly any manner desired.
• the fibers are essentially continuous and are either aligned unidirectionally, woven as a 2-dimensional fabric or shaped as a 3-dimensional reinforced preform.
• Such versatility in architecture is another advantage of the present composite system over prior art composites.
• the fibers of this invention may also be provided with a coating to toughen the composite by preventing bonding and chemical reactions between the fibers and the matrix. This allows the fibers to debond and pullout under stress such that the composite does not undergo catastrophic failure as demonstrated by ceramic monoliths.
• a coating to toughen the composite by preventing bonding and chemical reactions between the fibers and the matrix. This allows the fibers to debond and pullout under stress such that the composite does not undergo catastrophic failure as demonstrated by ceramic monoliths.
• any interfacial coating which has the above effect and which is compatible with the fiber and the matrix may be used herein. These include, for example, coatings of carbon, boron nitride, silicon carbide, silicon nitride, aluminum nitride, and combinations of the above. Such coatings and methods for their deposition are well known in the art. For instance, Corbin et al. in U.S. Pat.
• the coatings of the invention are generally used in thicknesses which allow the fibers to debond and pullout under stress. Although the thickness is dependent on coating quality, typical thicknesses are generally in the range of about 0.05 to about 1.0 micrometer.
• boron nitride coatings or coating combinations which contain boron nitride.
• the present inventors have discovered that when fibers with such coatings are incorporated within the matrix of the present invention they have novel long-term stability at elevated temperature in air. This was particularly unexpected since boron nitride coated fibers are known to undergo oxidative degradation under such conditions. Thus, the composites of the present invention retain their properties under conditions which adversely affect the prior art composites.
• the matrix precursor material to be used herein is modified hydrogen silsesquioxane resin (H-resin).
• Hydrogen silsesquioxane resin is formed by the hydrolysis or partial hydrolysis of HSiX 3 , wherein X is a hydrolyzeable substituent.
• exemplary hydrolyzable substituents include halogens such as chlorine, fluorine, bromine and the like and hydrocarbonoxy groups such as alkoxy, acyloxy and the like.
• these resins may be fully condensed (HSiO 3/2 ) n or they may be only partially hydrolyzed (i.e., containing some Si--X) and/or partially condensed (i.e., containing some Si--OH).
• these resins may contain a small number (eg., less than about 10%) of silicon atoms which have either 0 or 2 hydrogen atoms attached thereto due to various factors involved in their formation or handling.
• hydrogen silsesquioxane resin used in this invention is generally modified to render it useful in the formation of ceramic composites. Without modification, hydrogen silsesquioxane resin has a broad molecular weight range which can lead to a wide variability in the physical properties of the resin which, in turn, lead to variability in processing. Additionally, the broad molecular weight range of the resin can lead to decreased ceramic yields due to vaporization of low molecular weight species.
• the present inventor therefore, has discovered a method for tailoring the molecular weight distribution of the resin to eliminate these problems.
• This tailoring affords one the ability to make resins having, for instance, the appropriate rheological properties needed for ceramic fabrication techniques such as cloth lay-up of ceramic matrix composites, RTM of ceramic matrix composites and reinfiltration of porous ceramic bodies.
• the modification renders the resin curable under moderate conditions such as mild heat, radiation, curing catalysts or curing agents. This curability is essential to the invention to increase the ceramic yield and to inhibit the composite from delaminating during pyrolysis.
• the H-resin modification is performed by encapping the resin with a material containing Si--C and Si--H bonds.
• materials are those generally encompassed by the structure (R 1 R 2 R 3 Si) 2 O, wherein R 1 , R 2 , and R 3 are independently selected from hydrogen, alkyls such as methyl, ethyl, propyl and the like or aryls such as phenyl.
• R 1 , R 2 , and R 3 are independently selected from hydrogen, alkyls such as methyl, ethyl, propyl and the like or aryls such as phenyl.
• Specific compounds include tetramethyldisiloxane, hexamethyldisiloxane and the like.
• the endcapping and molecular weight control is generally accomplished by redistribution under acid/water conditions in the presence of the endcapping agent.
• the ratio of the H-resin to endcapping agent in this reaction can be used to tailor the molecular weight of the resin.
• the molar ratio of H-resin to endcapping agent is in the range of about 10:1 to about 1:10.
• modified hydrogen silsesquioxane resin is used to describe these endcapped resins which are curable and have tailored molecular weights.
• the Mn for these materials are in the range of about 500 to about 2500.
• SiO 2 in-situ silica
• the composites of the present invention may also contain fillers.
• Fillers are used herein to decrease the amount of matrix shrinkage which occurs on pyrolysis so that the resultant composites have lower porosity.
• Suitable fillers are known in the art and can include, for example, powders, whiskers or particulates of Al2O3, SiO2, other metal oxides, silicon carbide, silicon nitride, silicon hexaboride, aluminum nitride, boron nitride and the like.
• the preferred fillers to be used herein are boron nitride, silicon carbide, silicon nitride, and aluminum nitride.
• Such fillers are generally included in amounts up to about 80 volume percent based on the volume of modified H-resin material.
• the composites of this invention may also contain materials which assist in curing (crosslinking) the H-resin.
• These curing agents may be activated by heating the green body containing the curing agent to temperatures in the range of 50°-300° C. (i.e., the activation of a free radical precursor) or they may be crosslinked at room temperature.
• Curing agents are well known in the art. Examples include free radical precursors such as organic peroxides (dibenzoyl peroxide, bis-p-chlorobenzol peroxide, bis-2,4-dichlorobenzol peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butyl perbenzoate, 2,5-bis(t-butylperoxy)-2,3-dimethylhexane and t-butyl peracetate); and platinum-containing curing agents such as platinum metal, H 2 PtCl 6 , and ((C 4 H 9 ) 3 P) 2 PtCl 2 . Other conventional curing agents known in the art may also be used.
• organic peroxides dibenzoyl peroxide, bis-p-chlorobenzol peroxide, bis-2,4-dichlorobenzol peroxide, di-t-butyl peroxide, dicumyl peroxide, t-buty
• the curing agent is present in an effective amount, i.e. an amount sufficient to induce crosslinking in the H-resin. Normally, however, the peroxide curing agent will be present at about 0.1 to 5.0 weight percent based on the weight of the compound to be cured with the preferred amount being about 2.0 weight percent. When platinum-containing curing agents are used, the amount will normally be such that platinum is present at about 1 to 1000 ppm based on the weight of the compound to be cured with the preferred amount being about 50 to 150 ppm platinum.
• crosslinking agents include, for example, polyfunctional organosilicon compounds such as silanes, silazanes or siloxanes.
• the preferred crosslinking agents are organosilicon compounds with Si--H or Si--Vi functional bonds.
• the composites herein are produced by polymer infiltration.
• This process comprises first impregnating the coated fibers with a liquid preceramic mixture comprising the modified H-resin and, if desired, fillers.
• This preceramic mixture can be formed by either a solution or melt route.
• the modified H-resin and fillers are mixed in an organic solvent.
• the preferred solvents are those with a low vaporization point (such as lower than about 125° C.) at atmospheric pressure to facilitate removal from the impregnated fibers and those with less than about 1 percent by weight water.
• suitable organic solvents include aliphatic hydrocarbons such as hexane, heptane etc. and aromatic hydrocarbons such as benzene, toluene, etc.
• concentration of H-resin in solution can be varied over a wide range with higher concentrations generally resulting in larger amounts of the preceramic polymer impregnating the fiber.
• concentrations in the range of about 30 to about 60 weight percent are employed herein.
• the modified H-resin is heated no a temperature above its melting point yet below its curing temperature in an inert environment to form the preceramic mixture.
• Fillers may also be mixed in the molten polymer if desired.
• the fibers are then impregnated with the preceramic mixture by any convenient means.
• the fibers can be immersed in the mixture, sprayed with the mixture, held under a stream of the mixture, etc.
• the impregnated fibers can additionally be manipulated to uniformly distribute the matrix mixture in the fibers. Following impregnation, any excess matrix mixture on the fibers is allowed to drain off.
• pre-preg The resultant fibers which have been impregnated and the solvent evaporated are commonly called a "pre-preg".
• the impregnated fibers can merely be cooled to form the "pre-preg".
• the melt impregnated fibers may be formed prior to cooling by a process such as filament winding or pulltrusion. When these formed fibers are cooled, they can be immediately cured and fired as set forth below.
• the prepregs formed above may, optionally, be partially cured so that they will hold the shape imparted in a subsequent step.
• This partial curing also called “B-staging”
• This partial curing is generally accomplished by heating in air at a temperature in the range of about 50°to about 150° C. for about 2 minutes to about 4 hours. Generally, heating at about 100° C. for 10 to 15 minutes is sufficient.
• This heating may be conducted by any appropriate means, but the use of an air convection oven or similar equipment is usually sufficient. Care should be taken during this curing step to avoid temperature and time combinations which result in excessive curing such that flowability of the resin in the later molding or pressing steps is significantly reduced.
• the prepreg is then subjected to externally applied pressure while heating to form the composite into the desired shape and cause uniformity of resin about the fibers.
• This is accomplished by pressing the prepreg into a mold at a temperature and pressure which allows the resin to flow throughout the mold.
• the pressing conditions generally used include temperatures in the range of about 60°to about 300° C., pressures in the range of about 0.07 to 175 kg/cm 2 , and times in the range of about 2 minutes to about 6 hours. Pressing at about 175°C., 14-28 kg/cm 2 and 30 to 180 minutes generally provides satisfactory results. Temperatures and pressures which result in resin being forced out of the mold should be avoided.
• the formed prepreg is next infusibilized (cured) to insure complete or nearly complete crosslinking such that deformation on pyrolysis will not occur.
• Any schedule which produces the desired result may be used so long as the temperature does not cause ceramification.
• a preferred schedule comprises heating at less than 5° C./minute to 285° C. and then holding for 16 hours. This curing step may be performed in the mold under pressure or it may be accomplished in a conventional oven under nitrogen without any applied pressure.
• the pressed and cured product (green composite or molded part) is then slowly fired in a furnace to a temperature of at least 1000° C. in an inert atmosphere or vacuum until the product ceramifies. It is preferred that the green composite be fired an a temperature of about 1200° C.
• slow firing it is meant that the composites are heated in a slow (eg., 2° C./min), stepwise or linear fashion until the majority of any higher boiling volatiles present escape the composite after which time the temperature can be quickly raised to the ultimate firing temperature.
• the temperature for most composites should be raised to about 300° C. and the heating slowly continued until a temperature of about 800° C. is reached after which the temperature can be raised rather quickly to the ultimate firing temperature.
• the composite After completion of the firing process the composite is cooled. At least the initial cooling should also be under an inert atmosphere. When cooled, the resulting material is a uniform, hard, strong fiber reinforced composite.
• the volume percentage of fibers in the resulting composite can vary over a wide range depending on the desired use. Generally, it is preferred that about 10 to 65 volume percent of the composite is fiber.
• the composites formed by the above process are generally quite porous. Since it may be preferred to produce dense objects (which have higher strength), it is within the scope of this invention to reimpregnate the composites formed above. This is accomplished by merely impregnating the composite with the preceramic matrix mixture (without fillers) as described above (by either the solution or melt route), curing the reimpregnated composite and then firing. This "reimpregnation" can be repeated until products with the desired density and strength are achieved.
• the composites herein have many desirable properties such as good oxidation resistance at high temperatures, high strength and toughness, and a wide range of dielectric properties.
• the four-point flexural strength of the composites measured at room temperature and at temperatures up to 1100° C. in air generally exceed 2100 kg/cm 2 and often exceed 3500 kc/cm 2 .
• the tangent modulus of these composites often exceed 700,000 kg/cm 2 .
• Me represents a methyl group
• Ph represents a phenyl group
• Vi represents a vinyl group
• GPC Gel permeation chromatography
• Carbon, hydrogen and nitrogen analysis were done on a Control Equipment Corporation 240-XA Elemental Analyzer.
• Oxygen analyses were done on a Leco Oxygen Analyzer equipped with an Oxygen Determinator 316 (Model 783700) and an Electrode Furnace EF100. Silicon was determined by a fusion technique which consisted of converting the silicon material to soluble forms of silicon and analyzing the solute for total silicon by atomic absorption spectrometry.
• a toluene solution (approximately 20% by weight solids) of hydrogen silsesquioxane resin, 265 g (53 g of hydrogen silsesquioxane resin), was placed in a 500 mL three necked round bottom flask fitted with an overhead stirrer, thermometer and condenser under argon. To this solution was added 67 g of (Me 2 HSiO) 2 (one equivalent of (Me 2 HSiO) 0 .5, 1 g of trifluoroacetic acid and 1 g of water. The resulting solution was refluxed 24 h. The reaction was cooled and 1 g of CaCO 3 and 5 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 8 h period.
• the reaction was cooled and 5 g of Me 2 HSiCl added and allowed to stir overnight.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 85.3% and the ceramic analysis was C:9.3; Si:43.9; O:40.95.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures. The % weight change was found to be 0.5% and the material had the following ceramic analysis was C:8.3; Si:37.5; O:41.95.
• a toluene solution (approximately 20% by weight solids) of hydrogen silsesquioxane resin, 650 g (130 g of hydrogen silsesquioxane resin), was placed in a 1 L three necked round bottom flask fitted with an overhead stirrer, thermometer and condenser under argon. To this solution was added 160 g of (Me 2 HSiO) 2 (2.38 equivalents of (Me 2 HSiO), 2.5 g of trifluoroacetic acid and 2.5 g of water. The resulting solution was refluxed 48 h. The reaction was cooled and 2.5 g of CaCO 3 and 10 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 24 h period.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C. The yield was 222 g.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 71.2% and the ceramic analysis was C:15.1; Si:45.5; O:33.4.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures. The % weight change was found to be +1.1% and the material had the following ceramic analysis C:11.9; Si:42.5; O:37.5.
• the reaction was cooled and 2.0 g of CaCO 3 and 10 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 24 h period.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C. The yield was 160 g.
• the polymer has a Tg of 29° C.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 88.7% and the ceramic analysis was C:6.93; Si:46.3; O:42.5.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures.
• the % weight change was found to be +1.1% and the material had the following ceramic analysis C:5.6; Si:44.2; O:45.2.
• the reaction was cooled and 2.0 g of CaCO 3 and 10 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 24 h period.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C. The yield was 179 g.
• the polymer has a Tg of -39° C.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 89.6% and the ceramic analysis was C:10.17; Si:48.7; O:35.8.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures. The % weight change was found to be +0.8% and the material had the following ceramic analysis C:9.08; Si:42.3; O:40.3.
• a toluene solution (approximately 18% by weight solids) of hydrogen silsesquioxane resin 796 g (143 g of hydrogen silsesquioxane resin), was placed in a 1 L three necked round bottom flask fitted with an overhead stirrer, thermometer and condenser under argon. To this solution was added 20.1 g of (Me 2 HSiO) 2 (0.3 equivalents of (Me 2 HSiO) 0 .5, 2.0 g of trifluoroacetic acid and 2.0 g of water. The resulting solution was refluxed 40 h. The reaction was cooled and 2.0 g of CaCO 3 and 10 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 24 h period.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C. The yield was 160 g.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 89% and the ceramic analysis was C:6.93; Si:46.3; O:42.5.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures.
• the % weight change was found to be +1.1% and the material had the following ceramic analysis C:5.57; Si:44.2; O:45.2.
• a toluene solution (approximately 18% by weight solids) of hydrogen silsesquioxane resin 650 g (117 g of hydrogen silsesquioxane resin), was placed in a three necked round bottom flask fitted with an overhead stirrer, thermometer and condenser under argon. To this solution was added 160 g of (Me 2 HSiO) 2 (2.4 equivalents of (Me 2 HSiO) 0 .5, 2.0 g of trifluoroacetic acid and 2.0 g of water. The resulting solution was refluxed 48 h. The reaction was cooled and 2.0 g of CaCO 3 and 10 g of water were added to neutralize the acid.
• the flask was fitted with a Dean Stark trap and the water was removed by azetroping dry over an 24 h period.
• the polymer was isolated by filtration through a 1.0 micrometer membrane and removing the solvent in vacuo at 50° C. The yield was 70 g.
• the above mixture was heated to 150° C. under Ar to afford a brittle solid in 99% yield.
• An aliquot of this cured material was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The furnace was continuously purged with argon and the sample heated to 1200° C. at 10° C./minute and held at temperature for 1 hour before cooling back to ambient temperatures.
• the ceramic yield was 71.2% and the ceramic analysis was C:15.1; Si:45.5; O:33.4.
• the above ceramic was ground in a synthetic sapphire mortar and pestle to a fine powder. An aliquot of this powder was then weighed in an alumina boat and transferred to a Lindberg tube furnace. The sample was heated to 1000° C. at 10° C./minute in flowing air and held at temperature for 10 hours before cooling back to ambient temperatures. The % weight change was found to be +1.1% and the material had the following ceramic analysis C:11.9; Si:42.5; O:37.5.
• the cured plate had a thickness of 0.35 mm/ply and a weight of 16.66 g.
• the plate was pyrolyzed to 1200° C. under an inert atmosphere.
• the composite was densified to about 5% open porosity by 5 reinfiltration cycles comprising impregnation with an 80:20 mixture of the modified H-resin polymer of Example 6:vinyl functional siloxane fluid of the formula (MeSiO 1 .5) 0 .10 (MeViSiO) 0 .90 with 1 part Lupersol 101® followed by pyrolysis to 1200° C. under argon.
• Testing of the composite in a 3 point flexural test gave a strength of 1596 kg/cm 2 and a flexural modulus of 511,000 kg/cm 2 .
• the cured plate had a thickness of 0.38 mm/ply and a weight of 45.8 g.
• the plate was pyrolyzed to 1200° C. under an inert atmosphere.
• the pyrolyzed plate had a thickness of 0.35 mm/ply, a weight of 44.78 g, an apparent porosity of 21.1% and a density of 1.95 g/cc.
• the composite was densified to about 5% open porosity by 5 reinfiltration cycles comprising impregnation with an 80:20 mixture of the modified H-resin polymer of Example 6:vinyl functional siloxane fluid of the formula (MeSiO 1 .5) 0 .10 (MeViSiO) 0 .90 with 1 pare Lupersol 101® followed by pyrolysis to 1200° C. under argon. Testing of the composite in a 3 point flexural test gave a strength of 1820 kg/cm 2 . A test sample of this composite was oxidized at 1100° C. for 50 hours and had a weight change of +0.19% and gave a flexural strength of 1645 kg/cm 2 .
• the cured plate had a thickness of 0.35 mm/ply and a weight of 40.17 g.
• the plate was pyrolyzed to 1200° C. under an inert atmosphere.
• the pyrolyzed plate had a thickness of 0.33 mm/ply, a weight of 39.34 g, an apparent porosity of 21.1% and a density of 1.97 g/cc.
• the composite was densified to about 5% open porosity by 5 reinfiltration cycles comprising impregnation with an 80:20 mixture of the modified H-resin polymer of Example 6:vinyl functional siloxane fluid of the formula (MeSiO 1 .5) 0 .10 (MeViSiO) 0 .90 with 1 part Lupersol 101® followed by pyrolysis to 1200° C. under argon. Testing of the composite in a 3 point flexural test gave a strength of 2540 kg/cm 2 . A test sample of this composite was oxidized at 1100° C. for 50 hours and had a weight change of +0.19% and gave a flexural strength of 1876 kg/cm 2 .
• the cured plate was cut into 1.2 cm ⁇ 6.7 cm test samples.
• the test samples were pyrolyzed to 1200° C. under an inert atmosphere.
• the pyrolyzed plate had an apparent porosity of 21.1% and a density of 1.95 g/cc.
• the composite was densified by a reinfiltration cycles comprising impregnation with an 80:20 mixture of the modified H-resin polymer of Example 6:vinyl functional siloxane fluid of the formula (MeSiO 1 .5) 0 .10 (MeViSiO) 0 .90 with 1 part Lupersol 101® followed by pyrolysis to 1200° C. under argon.
• the porosity was found to be 13.5% and the test sample had a flexural strength of 1323 kg/cm 2 .
• the porosity was found to be 8% and the test sample had a flexural strength of 1778 kg/cm 2 .

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• 1996
  • 1996-04-30 CA CA002175433A patent/CA2175433A1/en not_active Abandoned
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